In Japanese Unexamined Patent Application Publication No. 2002-298310, a NiP alloy or a NiPW alloy is used as a gap layer. The NiP alloy or the NiPW alloy can be formed through plating, and three layers of a lower magnetic pole layer 21, a gap layer 22, and an upper magnetic pole layer 35 shown in the patent document can be continuously formed through plating, so that the miniaturization of a magnetic pole portion can be advanced further. As shown in FIG. 18, the etching rate of the NiPW alloy can be reduced to about 15 nm/Hr when the compositional ratio of the element W is 10 to 20 percent by mass. When the element W is controlled at about 48 percent by mass, the etching rate of the NiW alloy becomes about 25 nm/Hr. However, the NiPW alloy was a material which readily caused problems when used as the gap.
Japanese Unexamined Patent Application Publication No. 11-213332 discloses a metal film made of Re or the like or an alloy primarily composed of this metal film serving as a gap layer. No specific composition nor compositional ratio of the alloy prepared to contain Re is disclosed and, therefore, it is not clear whether the alloy film actually has the characteristics and properties desired in a gap layer.
Japanese Unexamined Patent Application Publication No. 2002-353222 discloses that a NiP—Re alloy is used as a barrier film of a thin film transistor, although this is not in the technical field of the thin film magnetic head. The content of Re is 50 to 75 percent. However, it was evident from the experiments described below that when the content of Re was this high, undesirable element diffusion readily occurred, particularly due to a heat treatment.
Japanese Unexamined Patent Application Publication No. 5-335314 discloses a Re-containing nickel alloy as a material used for one section of a semiconductor element.
Examples of characteristics and properties desired of a gap layer of a thin film magnetic head include non-magnetism, reduced element diffusion at the interface to a magnetic layer, and chemical agent resistance.
As a result of the experiments conducted by the present inventor, it was determined that the NiP alloy, was susceptible to an alkaline aqueous solution used in the slider processing and the like, and problems of elution and the like occurred when the NiP alloy was exposed to the alkaline aqueous solution. When the NiP alloy serving as a gap layer is eluted and, thereby, a space and the like are left behind, problems occur in that, for example, magnetic pole layers disposed on and under the gap layer are corroded from within the space, and become susceptible to damage during sliding on a recording medium. Therefore, it is desirable that the material used for the gap layer is resistant to the alkaline aqueous solution.
The NiP alloy becomes non-magnetic by appropriately controlling the compositional ratio of the element P. According to the experiments conducted by the present inventor, it was determined that the NiP alloy took on the magnetism after being heat-treated at 200° C. unless at least about 16 percent by mass of element P was contained. A heating step may be used in the process for manufacturing the thin film magnetic head, and it is desirable that the non-magnetism is maintained after a heat treatment is performed at about 200° C. or more.
It is known that the element P can be contained in an alloy at about 18 percent by mass at the maximum. As a result, in order to appropriately achieve the non-magnetization of the NiP alloy, the content of the element P must be controlled within a very narrow allowable range.